An upright vacuum cleaner typically comprises a main body containing dirt and dust separating apparatus, a cleaner head mounted on the main body and having a suction opening, and a motor-driven fan unit for drawing dirt-bearing air through the suction opening. The dirt-bearing air is conveyed to the separating apparatus so that dirt and dust can be separated from the air before the air is expelled to the atmosphere.
The suction opening is directed downwardly to face the floor surface to be cleaned. The separating apparatus can take the form of a filter, a filter bag or, as is known, a cyclonic arrangement. The present invention is not concerned with the nature of the separating apparatus and is therefore applicable to vacuum cleaners utilizing any of the above arrangements or another suitable separating apparatus.
A driven agitator, usually in the form of a brush bar, is supported in the cleaner head so as to protrude to a small extent from the suction opening. The brush bar comprises an elongate cylindrical core bearing bristles which extend radially outward from the core. Rotation of the brush bar causes the bristles to sweep along the surface of the carpet to be cleaned to loosen dirt and dust, and pick up debris. The suction of air causes air to flow underneath the sole plate and around the brush bar to help lift the dirt and dust from the surface of the carpet and then carry it from the suction opening through the cleaner head towards the separating apparatus.
The brush bar is normally driven by a motor and a drive belt connected to a shaft rotated by the motor. This brush bar may be driven by a dedicated brush bar motor, or it may be driven by the vacuum motor that powers the vacuum cleaner.
It is desirable to be able to bring the brush bar into and out of operation, for example depending on the type of floor surface to be cleaned. If the brush bar is driven by a dedicated motor, this motor may simply be switched off to deactivate the brush bar. On the other hand, if the agitator is driven by the vacuum motor a clutch assembly may be provided to transmit torque to the brush bar. When the brush bar is activated, the clutch is engaged so that torque generated by the motor is transmitted to the brush bar, whereas when the brush bar is deactivated the clutch is disengaged so that torque is not transmitted to the brush bar.
A problem which may be encountered with vacuum cleaners having such a brush bar is that, on occasion, the brush bar may become jammed if it becomes entangled with objects on the floor surface or if it is pressed hard on to the floor surface. This can overload the motor used to rotate the brush bar, which may lead to damage of the motor or the drive belt. When the brush bar is driven by a dedicated brush bar motor, it is relatively straightforward to sense that the brush bar has become jammed. For example, the rise in the current drawn by the brush bar motor, due to the increased torque required to rotate the brush bar, can be detected and the motor can be switched off if the current rise is above a threshold value. However, when the brush bar is driven by the vacuum motor the detection of such an overload condition can be more difficult and so one technique that has been proposed to limit the amount of torque applied to a jammed brush bar is to cause the drive belt to slip. While this can reduce the risk of damaging the vacuum motor, over time the drive belt can deteriorate and require replacement.
WO 2005/107553 describes a vacuum cleaner which uses a clutch assembly to transfer torque from the vacuum motor to the brush bar. The clutch assembly comprises an input clutch member connected to the vacuum motor by a first drive belt, and an output clutch member connected to the brush bar by a second drive belt. The clutch assembly comprises an actuator for disengaging the output clutch member from the input clutch member when there is a difference in their rotational speeds due to the jamming of the brush bar driven by the output clutch member. The actuator is activated by a temperature rise caused by friction between two contacting surfaces of the clutch assembly which are rotating at different speeds. When the user does not require the brush bar to rotate, for example when cleaning a hard floor surface, the user must manually disengage the clutch members. The clutch assembly is provided with a grip portion which the user manipulates to disengage the output clutch member from the input clutch member.
It is an aim of at least the preferred embodiment of the present invention to provide a clutch assembly for a surface treating appliance which can enable an agitator to be readily disengaged from a drive motor both when the brush bar becomes jammed and as required by a user, for example depending on the type of floor surface to be treated by the appliance.